Belt driving device, transfer device, and image forming apparatus

ABSTRACT

A belt driving device includes an annular belt member, rotary members, a protrusion, and a removing member. The rotary members extend in parallel and rotate. The belt member is wound around the rotary members. The protrusion protrudes from an inner peripheral surface of the bel member. The protrusion extends along an edge of the belt member. The protrusion and each rotary member are arranged in an extending direction of the rotary member. The removing member includes a plate-shaped portion. The plate-shaped portion is in contact with an outer peripheral surface of the belt member at a location where the removing member faces one of the rotary members with the belt member being interposed therebetween, so as to remove unnecessary matters from the outer peripheral surface of the belt member. The removing member extends to an outside of end portions of the rotary members in the extending direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2019-191933 filed Oct. 21, 2019.

BACKGROUND 1. Technical Field

The present disclosure relates to a belt driving device, a transfer device, and an image forming apparatus.

2. Related Art

There are devices in which an annular belt member is wound around plural rotary members and driven. In order to prevent positions where the belt member is wound on the rotary members from moving in a direction along shafts of the rotary members, some of the devices have such a configuration that a protrusion (for example, a rib) extending along an edge of the belt member is provided.

JP-A-2002-333779 discloses an image forming apparatus in which a transfer belt includes a rib in a circumferential direction at an end portion in a width direction in order to prevent the belt from shifting, and a stretch roller having the largest length, in the width direction, of a portion where the stretch roller is in contact with the transfer belt is a follower roller.

SUMMARY

Aspects of non-limiting embodiments of the present disclosure relate to preventing damage to a belt member caused by a protrusion riding on a rotary member.

Aspects of certain non-limiting embodiments of the present disclosure address the above advantages and/or other advantages not described above. However, aspects of the non-limiting embodiments are not required to address the advantages described above, and aspects of the non-limiting embodiments of the present disclosure may not address advantages described above.

According to an aspect of the present disclosure, there is provided a belt driving device including: an annular belt member; plural rotary members that extend in parallel and rotate, the belt member being wound around the rotary members, the belt member circulating; a protrusion that protrudes from an inner peripheral surface of the belt member, the protrusion extending along an edge of the belt member, the protrusion and each rotary member being arranged in an extending direction of the rotary member; and a removing member including a plate-shaped portion, in which the plate-shaped portion of the removing member is in contact with an outer peripheral surface of the belt member at a location where the removing member faces one of the rotary members with the belt member being interposed therebetween, so as to remove unnecessary matters from the outer peripheral surface of the belt member, and the removing member extends to an outside of end portions of the rotary members in the extending direction.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiment(s) of the present disclosure will be described in detail based on the following figures, wherein:

FIG. 1 is a schematic configuration diagram showing an image forming apparatus of a first exemplary embodiment;

FIG. 2 is a side view schematically showing a structure of a secondary transfer unit;

FIG. 3 is a top view schematically showing the structure of the secondary transfer unit;

FIG. 4 is a diagram schematically showing a structure around a cleaning blade;

FIG. 5 is a diagram schematically showing a structure around a cleaning blade according to a second exemplary embodiment of the present disclosure;

FIG. 6 is a diagram showing a boundary position between a central portion and an end portion;

FIG. 7 is a diagram schematically showing a structure around a cleaning blade according to a third exemplary embodiment of the present disclosure; and

FIG. 8 is a diagram schematically showing a structure around a cleaning blade according to a fourth exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

FIG. 1 is a schematic configuration diagram showing an image forming apparatus of a first exemplary embodiment.

An image forming apparatus 1 shown in FIG. 1 is a so-called tandem color printer. A sheet P is used as a recording material in the image forming apparatus 1. Plastic paper or an envelope other than the sheet P may be employed as the recording material. In the following description, the sheet P is used as a representative of the recording material.

The image forming apparatus 1 includes four image engines 10Y, 10M, 10C, and 10K corresponding to four colors of, for example, yellow (Y), magenta (M), cyan (C), and black (K). In the present exemplary embodiment, each of the image engines 10Y, . . . , 10K forms a toner image by a so-called electrophotogmphic process. In each of the image engines 10Y, . . . , 10K, the toner image of each color is formed on a corresponding one of photoconductor drums 11Y, 11M, 11C, 11K by sequentially performing the steps of charging, exposure, and development.

The image forming apparatus 1 in the present exemplary embodiment employs an indirect transfer method, and includes an intermediate transfer belt 30. The image forming apparatus 1 also includes a secondary transfer unit 50, a fixing device 60, and a sheet transport unit 80.

The intermediate transfer belt 30 is an endless belt stretched over support rollers 31 to 35. The intermediate transfer belt 30 circulates counterclockwise through the image forming units 10Y, 10M, 10C, and 10K and the secondary transfer unit 50.

The image engines 10Y, . . . , 10K have primary transfer rollers 15Y, 15M, 15C, and 15K at positions where the primary transfer rollers 15Y, 15M, 15C, and 15K face the photoconductor drums 11Y, . . . , 11K with the intermediate transfer belt 30 interposed therebetween. The primary transfer rollers 15Y, . . . , 15K cause the toner images on the photoconductor drums 11Y, . . . , 11K to be electrostatically attracted to the intermediate transfer belt 30 by receiving a voltage. The toner images of the colors formed by the image engines 10Y, . . . , 10K are sequentially transferred onto the intermediate transfer belt 30 in a superimposed manner by the primary transfer rollers 15Y, . . . , 15K. As a result of such transfer, a color image is formed on the intermediate transfer belt 30. The intermediate transfer belt 30 carries and moves the color image and transports the color image to the secondary transfer unit 50.

The secondary transfer unit 50 is provided such that the intermediate transfer belt 30 is interposed between the secondary transfer unit 50 and a backup roller 34 that is one of the support rollers 31 to 35. The secondary transfer unit 50 transfers the color image with the sheet P being interposed between the secondary transfer unit 50 and the intermediate transfer belt 30.

Sheets P are stored in a stacked state on a sheet tray T provided in a lower part of the image forming apparatus 1. The sheets P in the sheet tray T is taken out one by one from the sheet tray T by a feeding roller 81 provided in the sheet transport unit 80 and retard rollers 82, and is transported along a transport path R by transport rollers 83. Registration rollers 84 of the sheet transport unit 80 feed the sheet P to the secondary transfer unit 50 in accordance with timing of transporting the color image by the intermediate transfer belt 30.

As will be described in detail below, the secondary transfer unit 50 transfers the color image on the intermediate transfer belt 30 onto the sheet P by receiving a voltage. The secondary transfer unit 50 is an example of a belt driving device of the present disclosure, and is also an example of a transfer device of the present disclosure. The sheet P on which the color image is transferred by the secondary transfer unit 50 is transported to the fixing device 60 by the secondary transfer unit 50 and the transport rollers 83 of the sheet transport unit 80.

A combination of the image forming units 10Y, 10M, 10C, and 10K, the intermediate transfer belt 30, and the secondary transfer unit 50 corresponds to an example of an image forming unit according to the present disclosure. A combination of the secondary transfer unit 50 and the sheet transport unit 80 corresponds to an example of a transport unit according to the present disclosure.

The fixing device 60 fixes the color image on the sheet P by applying heat and pressure to the sheet P. The sheet P on which the color image is fixed by the fixing device 60 is fed to the outside of the image forming apparatus 1 by delivery rollers 86 provided in the sheet transport unit 80.

The secondary transfer unit 50 will be described in more detail below.

FIGS. 2 and 3 are diagrams schematically showing a structure of the secondary transfer unit. FIG. 2 is a side view and FIG. 3 is a top view. For convenience of explanation, FIG. 3 shows the structure in which the inside of the secondary transfer unit is seen through.

The secondary transfer unit 50 includes a transfer roller 51, a separation roller 52, and an endless transfer belt 53 wound around the transfer roller 51 and the separation roller 52. The secondary transfer unit 50 is unitized by assembling elements in a transfer unit support frame 501. The transfer roller 51 and the separation roller 52 include rotation shafts 511 and 521. The rotation shafts 511 and 521 are rotatably supported by the transfer unit support frame 501. The transfer roller 51 and the separation roller 52 correspond to an example of plural rotary members of the present disclosure. The transfer belt 53 corresponds to an example of a belt member of the present disclosure.

The transfer roller 51 is driven by a transfer motor 56 to rotate clockwise to drive the transfer belt 53. The transfer belt 53 is a resin belt having low elasticity and circulates clockwise by receiving a driving force by the transfer roller 53.

The transfer roller 51 presses the transfer belt 53 against the intermediate transfer belt 30 from the inside of the transfer belt 53. When the sheet P is fed between the transfer belt 53 and the intermediate transfer belt 30 pressed against each other, the sheet P is transported in a circulation direction while being interposed between the transfer belt 53 and the intermediate transfer belt 30. The transfer roller 51 is connected to a power supply (not shown), and a transfer bias is applied to the transfer roller 51 from the power supply. By the action of the transfer bias, the color image on the intermediate transfer belt 30 is transferred onto the sheet P while the sheet P passes between the transfer belt 53 and the intermediate transfer belt 30.

The separation roller 52 is a roller having a diameter smaller than that of the transfer roller 51. Since the separation roller 52 abruptly bends a traveling direction of the transfer belt 53, a leading end of the sheet P placed on the transfer belt 53 is separated from the transfer belt 53. In the present exemplary embodiment, the separation roller 52 is shorter in length than the transfer roller 51 and rotates following movement of the intermediate transfer belt 30.

At edges of the transfer belt 53, resin ribs 531 are provided. The ribs 531 prevent the transfer belt 53 from falling off the transfer roller 51. The rib 531 protrudes inward from an inner peripheral surface of the transfer belt 53. The rib 531 extends in a movement direction of the transfer belt 53 along the edge of the transfer belt 53. The ribs 531 and the transfer roller 51 are arranged in an extending direction of the rotation shaft 511. The ribs 531 and the separation roller 52 are arranged in an extending direction of the rotation shaft 521. In the present exemplary embodiment, the ribs 531 are provided on both sides of the transfer belt 53 across the transfer roller 51 and the separation roller 52. The rib 531 corresponds to an example of a protrusion of the present disclosure.

The secondary transfer unit 50 includes a cleaning blade 55. An edge of the cleaning blade 55 is in contact with an outer peripheral surface of the transfer belt 53. A position of the cleaning blade 55 is fixed with respect to the transfer unit support frame 501. The edge of the cleaning blade 55 rubs against the outer peripheral surface of the transfer belt 53 with the movement of the transfer belt 53. The toner and other contaminants adhering to the transfer belt 53 are rubbed by the cleaning blade 55 and scraped off from the transfer belt 53.

The cleaning blade 55 is provided at a position where the cleaning blade 55 faces the transfer roller 51 with the transfer belt 53 being interposed therebetween. The cleaning blade 55 prevents the ribs 531 of the transfer belt 53 from riding on the transfer roller 51.

FIG. 4 is a diagram schematically showing a structure around the cleaning blade.

For convenience of description, FIG. 4 shows a cross section of the transfer roller 51 and the transfer belt 53.

The cleaning blade 55 includes a rubber first portion 551 having a plate-shaped outer shape, and a metal second portion 552 holding the first portion 551. An edge of the first portion 551 is in contact with the outer peripheral surface of the transfer belt 53 to remove unnecessary matters. A length of the cleaning blade 55 in the extending direction of the transfer roller 51 is longer than that of the transfer roller 51. End portions of the cleaning blade 55 reach further outside than end portions of the transfer roller 51.

The transfer belt 53 is driven by the transfer roller 51 to circulate as described above. The transfer belt 53 may deviate, that is, so called “walk” may occur. Due to the walk, a traveling position of the transfer belt 53 during the circulation deviates in the extending direction of the transfer roller 51 intersecting with the circulation direction. FIG. 4 shows a state in which the transfer belt 53 deviates to the left side of the figure and comes close to a wall of the transfer unit support frame 501 supporting the rotation shaft 511.

When the transfer belt 53 deviates in this manner, the rib 531 comes into contact with the end portion of the transfer roller 51 to reduce the deviation. In a case where the transfer belt 53 largely deviates due to the walk, a part of the rib 531 may ride on the end portion of the transfer roller 51 while being in contact with the end portion of the transfer roller 51. When the rib 531 rides on the transfer roller 51 in this manner, a force that pushes back the transfer belt 53 acts such that the traveling position of the transfer belt 53 returns toward a center of the transfer belt 53. When the rib 531 rides on the transfer roller 51, a strong bending stress or the like is applied to the transfer belt 53. Accordingly, the transfer belt 53 may be damaged when the rib 531 rides on the transfer roller 51 repeatedly.

When the rib 531 rides on the transfer roller 51 frequently, the edge of the cleaning blade 55 is pushed up, which may cause a cleaning failure.

In the present exemplary embodiment, since the cleaning blade 55 is long as described above, an edge portion of the transfer belt 53 is pressed by the force with which the edge of the cleaning blade 55 is in contact with the outer peripheral surface of the transfer belt 53, and riding of the rib 531 onto the transfer roller 51 is prevented. A location where the cleaning blade 55 presses the transfer belt 53 is a part of the entire circumference of the transfer belt 53. However, when the transfer belt 53 deviates until the rib 531 comes into contact with the end portion of the transfer roller 51, the force that pushes back the transfer belt 53 acts strongly at the location, and the traveling position of the transfer belt 53 returns toward the center of the transfer belt 53. Therefore, the frequency at which the rib 531 rides on the end portion of the transfer roller 51 is reduced. As a result, damage to the transfer belt 53 is prevented and the cleaning failure is also prevented.

Since the transfer roller 51 is a driving roller driven by the transfer motor 56, a force that changes the traveling position of the transfer belt 53 in the extending direction of the transfer roller 51 is stronger than that of the separation roller 52 that rotates following the transfer belt 53. Since the cleaning blade 55 is provided at the position where the cleaning blade 55 faces such a driving roller, the force that pushes back the transfer belt 53 strongly acts when the rib 531 comes into contact with the end portion of the transfer roller 51, and the riding of the rib 531 is strongly prevented.

Since the transfer roller 51 is a roller having a diameter larger than that of the separation roller 52, the force that changes the traveling position of the transfer belt 53 in the extending direction of the transfer roller 51 is stronger than that of the separation roller 52. Also, since the cleaning blade 55 is provided at the position where the cleaning blade 55 faces such a large-diameter roller, the force that pushes back the transfer belt 53 strongly acts when the rib 531 comes into contact with the end portion of the transfer roller 51, and the riding of the rib 531 is strongly prevented.

Further, since the transfer roller 51 is a roller longer than the separation roller 52, the force that changes the traveling position of the transfer belt 53 in the extending direction of the transfer roller 51 is stronger than that of the separation roller 52. Also, since the cleaning blade 55 is provided at the position where the cleaning blade 55 faces such a long roller, the force that pushes back the transfer belt 53 strongly acts when the rib 531 comes into contact with the end portion of the transfer roller 51, and the riding of the rib 531 is strongly prevented.

Next, a second exemplary embodiment of the present disclosure will be described. Since the second exemplary embodiment is the same as the first exemplary embodiment except that a structure of the cleaning blade 55 is different, the description will be focused on differences from the first exemplary embodiment and a repetitive description will be omitted.

FIG. 5 is a diagram schematically showing a structure around a cleaning blade according to the second exemplary embodiment of the present disclosure.

In the second exemplary embodiment, a shape of a second portion 552 of the cleaning blade 55 is different from that of the first exemplary embodiment. That is, the second portion 552 at an end portion 553 in the extending direction of the transfer roller 51 protrudes toward the transfer belt 53 and a distance between the second portion 552 and the transfer belt 53 is shorter at the end portion 553 than that at a central portion 554. That is, protrusion of the first portion 551 toward the transfer belt 53 is smaller at the end portion 553 than at the central portion 554.

As a result, rigidity of the cleaning blade 55 including the first portion 551 and the second portion 552 is higher at the end portion 553 than that at the central portion 554. Also, the strength with which the cleaning blade 55 is in contact with an outer peripheral surface of the transfer belt 53 is stronger at the end portion 553 than that at the central portion 554. Therefore, the riding of the rib 531 is strongly prevented at the end portion 553, and high cleaning performance is obtained by contact pressure suitable for cleaning the transfer belt 53 at the central portion 554.

Here, a boundary position between the central portion 554 and the end portion 553 will be discussed.

FIG. 6 is a diagram showing a boundary position between a central portion and an end portion.

A boundary B between the central portion 554 and the end portion 553 is located near an end portion of the transfer roller 51 in the extending direction of the transfer roller 51. More specifically, on the basis of a position P0 at the end portion of the transfer roller 51, the boundary B is located on an inner side of a first location P1. The first location P1 is located on an outer side of the position P0 of the end portion and at a distance d from the position P0. The distance d is equal to a width d of the rib 531. Accordingly, the cleaning blade 55 is in strong contact with the outer peripheral surface of the transfer belt 53 at a location where the rib 531 rides on the transfer roller 51, and the riding of the rib 531 is strongly prevented.

Further, on the basis of the position P0 of the end portion of the transfer roller 51, the boundary B is located on an outer side of a second location P2. The second location P2 is located on an inner side of the position P0 of the end portion and at the distance d, which is equal to the width of the rib 531, from the position P0. Accordingly, the cleaning blade 55 is in contact with the outer peripheral surface of the transfer belt 53 with a strength suitable for cleaning, at a location where contribution of the rib 531 to the prevention of riding is low, and high cleaning performance is obtained.

Next, a third exemplary embodiment of the present disclosure will be described. Since the third exemplary embodiment is the same as the first exemplary embodiment except that a structure of the cleaning blade 55 is different, the description will be focused on differences from the first exemplary embodiment and a repetitive description will be omitted.

FIG. 7 is a diagram schematically showing a structure around a cleaning blade according to the third exemplary embodiment of the present disclosure.

In the third exemplary embodiment, a shape of the first portion 551 of the cleaning blade 55 is different from that of the first exemplary embodiment. That is, in the first portion 551, a thickness of an end portion 555 is larger than the other portions (that is, a central portion). As a result, the first portion 551 has higher rigidity at the end portion 555 than at the central portion. The cleaning blade 55 including the first portion 551 and the second portion 552 has higher rigidity at the end portion than at the central portion. Also, the strength with which the cleaning blade 55 is in contact with an outer peripheral surface of the transfer belt 53 is stronger at the end portion than at the central portion.

Accordingly, in the third exemplary embodiment, similarly to the second exemplary embodiment, the riding of the rib 531 is strongly prevented at the end portion of the cleaning blade 55, and high cleaning performance is obtained by contact pressure suitable for cleaning the transfer belt 53 at the central portion of the cleaning blade 55.

Next, a fourth exemplary embodiment of the present disclosure will be described. Since the fourth exemplary embodiment is the same as the first exemplary embodiment except that a structure of the cleaning blade 55 is different, the description will be focused on differences from the first exemplary embodiment and a repetitive description will be omitted.

FIG. 8 is a diagram schematically showing a structure around a cleaning blade according to the fourth exemplary embodiment of the present disclosure.

In the fourth exemplary embodiment, the first portion 551 of the cleaning blade 55 has been subjected to surface treatment using, for example, diamond like carbon. The surface treatment hardens the surface of the first portion 551 and reduces friction with the transfer belt 53. Accordingly, the cleaning blade 55 has a longer life. An end portion 556 of the first portion 551 has been subjected to the surface treatment in a region wider than a central portion 557. Therefore, the end portion 556 of the first portion 551 has higher rigidity than the central portion 557, and contact pressure with the outer peripheral surface of the transfer belt 53 is higher at the end portion 556.

Accordingly, in the fourth exemplary embodiment, similarly to the second exemplary embodiment, the riding of the rib 531 is strongly prevented at the end portion of the cleaning blade 55 and the high cleaning performance is obtained by the contact pressure suitable for cleaning the transfer belt 53 at the central portion of the cleaning blade 55.

The above description shows the examples in which a removing member of the present disclosure extends to outsides of end portions of the rotary member of the present disclosure at both edges of the belt member of the present disclosure. Alternatively, the removing member of the present disclosure may extend to an outside of one of the end portions of the rotary member where, for example, the protrusion has a strong tendency of riding due to the walk.

The above description shows the examples in which the belt driving device of the present disclosure is applied to the transfer device. Alternatively, the belt driving device of the present disclosure may be applied to a unit that drives the intermediate transfer belt or a device that drives the sheet transport belt.

In the above description, the color printer is shown as an exemplary embodiment of the image forming apparatus of the present disclosure. Alternatively, the image forming apparatus of the present disclosure may be a monochrome printer, or may be a copier, a facsimile, or a multifunction device.

In the above exemplary embodiments, the electrophotographic image forming apparatuses have been described as examples. It is noted that the present disclosure is applicable to transfer devices and image forming apparatuses that are of types other than the electrophotographic type. For example, the present disclosure may be applied to an inkjet image forming apparatus. Specifically, the present disclosure may be applied to an image forming apparatus that draws an ink image on an intermediate transfer body using an ink ejection head and transfers the ink image from the intermediate transfer body onto a sheet. As in the electrophotographic image forming apparatus, the inkjet image forming apparatus reduces impact and wind pressure from a sheet and prevents ink from spattering and moving on the intermediate transfer body.

The present disclosure may be applied to an image forming apparatus of another type so long as the image forming apparatus transfers an image onto a recording material.

The present disclosure may be applied to a belt member, other than a transfer belt, in an image forming apparatus. For example, the present disclosure may be applied to a transport device between a transfer device and a fixing device.

The present disclosure may be applied to a belt driving device other than an image forming apparatus.

The present disclosure is made for the purpose of addressing the problems described in the “SUMMARY” section. It is noted that the configurations of the present disclosure are not prevented from being diverted to other purposes in a form that does not address the problem. A form in which any of the configurations of the present disclosure is diverted in this manner is also an exemplary embodiment of the present disclosure.

The foregoing description of the exemplary embodiments of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical applications, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents. 

What is claimed is:
 1. A belt driving device comprising: an annular belt member; a plurality of rotary members that extend in parallel and rotate, the belt member being wound around the rotary members, the belt member circulating: a protrusion that protrudes from an inner peripheral surface of the belt member, the protrusion extending along an edge of the belt member, the protrusion and each rotary member being arranged in an extending direction of the rotary member; and a removing member comprising a plate-shaped portion, wherein the plate-shaped portion of the removing member is in contact with an outer peripheral surface of the belt member at a location where the removing member faces one of the rotary members with the belt member being interposed therebetween, so as to remove unnecessary matters from the outer peripheral surface of the belt member, and the removing member extends to an outside of end portions of the rotary members in the extending direction.
 2. The belt driving device according to claim 1, wherein an end portion of the removing member in the extending direction is in stronger contact with the outer peripheral surface than a central portion of the removing member in the extending direction.
 3. The belt driving device according to claim 1, wherein an end portion of the removing member in the extending direction has higher rigidity than a central portion of the removing member in the extending direction.
 4. The belt driving device according to claim 2, wherein the end portion of the removing member is harder than at the central portion of the removing member, due to partial surface treatment.
 5. The belt driving device according to claim 4, wherein the removing member has been subjected to the surface treatment at a contact portion with the belt member.
 6. The belt driving device according to claim 2, wherein the removing member comprises a first portion that is in contact with the outer peripheral surface of the belt member, and a second portion that holds the first portion and has a higher rigidity than the first portion, and the second portion has a shorter distance to the outer peripheral surface at the end portion than at the central portion.
 7. The belt driving device according to claim 2, wherein the removing member is thicker at the end portion than at the central portion.
 8. The belt driving device according to claim 2, wherein a boundary between the central portion and the end portion of the removing member is located on an inner side relative to a first location, and the first location is located on an outer side, in the extending direction, of an end surface position of the one of the rotary members and is located at a distance equal to a width of the protrusion.
 9. The belt driving device according to claim 2, wherein a boundary between the central portion and the end portion of the removing member is located on an outer side of a second location, and the second location is located on an inner side, in the extending direction, of an end surface position of the one of the rotary members and is located at a distance equal to a width of the protrusion.
 10. The belt driving device according to claim 1, wherein the one of the rotary members is a rotary member having the largest force that changes a position of the belt member in the extending direction among the plurality of rotary members.
 11. The belt driving device according to claim 10, wherein the one of the rotary members has the largest length in the extending direction among the plurality of rotary members.
 12. The belt driving device according to claim 10, wherein the one of the rotary members is the thickest rotary member among the plurality of rotary members.
 13. The bell driving device according to claim 10, wherein the one of the rotary members drives the removing member by rotating under a driving force.
 14. The belt driving device according to claim 11, wherein the one of the rotary members drives the removing member by rotating under a driving force.
 15. The belt driving device according to claim 12, wherein the one of the rotary members drives the removing member by rotating under a driving force.
 16. A transfer device comprising: an annular belt member comprising an outer peripheral surface, the annular belt member being configured to transfer an image onto a recording material by (i) the outer peripheral surface coming into contact with the recording material and (ii) receiving a voltage; a plurality of rotary members that extend in parallel and rotate, the belt member being wound around the rotary members, the belt member circulating; a protrusion that protrudes from an inner peripheral surface of the belt member, the protrusion extending along an edge of the belt member, the protrusion and each rotary member being arranged in an extending direction of the rotary member; and a removing member having a plate-shaped outer shape, wherein a portion of the removing member, where the removing member faces one of the rotary members with the belt member being interposed therebetween, is in contact with the outer peripheral surface of the belt member, so as to remove unnecessary matters from the outer peripheral surface of the belt member, and the removing member extends to an outside of end portions of the rotary members in the extending direction.
 17. An image forming apparatus comprising: a transport unit configured to transport a recording material; an image forming unit configured to form an image on the recording material transported by the transport unit; and a belt driving device assembled to at least one of the transport unit or the image forming unit, wherein the belt driving device comprises an annular belt member, a plurality of rotary members that extend in parallel and rotate, the belt member being wound around the rotary members, the belt member circulating, a protrusion that protrudes from an inner peripheral surface of the belt member, the protrusion extending along an edge of the belt member, the protrusion and each rotary member being arranged in an extending direction of the rotary member, and a removing member having a plate-shaped outer shape, a portion of the removing member, where the removing member faces one of the rotary members with the belt member being interposed therebetween, is in contact with an outer peripheral surface of the belt member, so as to remove unnecessary matters from the outer peripheral surface of the belt member, and the removing member extends to an outside of end portions of the rotary members in the extending direction. 